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ok, so a jerry can made truck work great. Only scenerio i see, between the can and tank ARE not sharing, is the vent tube. Can the one off the tank, be pinched?
 

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ok, so a jerry can made truck work great. Only scenerio i see, between the can and tank ARE not sharing, is the vent tube. Can the one off the tank, be pinched?
If both the vents (there should be two of them) were closed off, your fuel tank would start collapsing, and with the shape of it, you'd probably see evidence of that (kinks at the corners, etc.)

Unless you've done the In-Tank mods, I'd suspect the screens in the mixing assembly inside the tank. See the pics that Machiner1 posted earlier in the thread. Those two slimey cylinders are actually filter screens - can't tell from the picture, but they are.
 

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Machinery, with 3 pages of threads, have you DONE the Hutch Mod?
Yes, he did. Did you read the three pages? (Actually he confirmed that up at the top of this page).
 

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Discussion Starter #45
I have done the hutch mod, replaced the pump twice, replaced the filter, rebuilt the FPR, added the FRX kit, Cleaned out the tank, and blew out and inspected all fuel lines. There is no evidence of fuel leakage, and I am not making oil. After about 3-6 minutes of driving, the fuel pressure will be at 40 psi at idle. I can remove the filler cap, check wiring, and jiggle hoses, but it has no effect on the pressure. My post filter sending unit has stopped working, so the only one I have to go by is the pre-filter one. (Don't buy Glowshift). I do trust the gauge, because the performance of the truck directly reflects the pressure readings.

The problem seems to be heat or run time related. When first started the pressure is great. after 3 minutes it is noticeably poor, and after 6 minutes it levels out at crappy, but never goes away completely. I have not and cannot stop driving the truck, I just have to drive it really softly, trying not to allow drops below 20psi.

I appreciated all of the help and input, and will keep pulling it in the garage at 2am every morning when I get home from work until I figure this out. I think my next step is going to be the gallon jug of fuel RT recommended. If I can at least positively rule out sections of the fuel system, I think I can focus in on the problem. You guys are great, and I love this truck, but im really hoping this thread doesn't get as long as the one about the 45mph bounce LOL.
 

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That won't work if there is a restriction in the inlet side. The FPR isn't the rate limiting factor in pressure - it's flow. Plus, he's already tried that.


Sent from AutoGuide.com App
 

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This is a good head scratcher.

Do you have a way to monitor voltage to the fuel pump while driving?

I had a fuel pump go bad, when I checked the voltage at idle (which the truck could barely hold) to the pump, it was 7.5VDC. Not good. . . .
 

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So a pump that is going bad can have a low voltage?
 

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Discussion Starter #50
This is a good head scratcher.

Do you have a way to monitor voltage to the fuel pump while driving?

I had a fuel pump go bad, when I checked the voltage at idle (which the truck could barely hold) to the pump, it was 7.5VDC. Not good. . . .
I will do this today. I checked all lines for kinks again last night, and everything looks fine.
 

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machiner...you've tried 2 pumps. And like you, tough to believe, both pumps are bad. However, i remember reading, a member having issues getting the appropriate 12v TO, the pump?
 

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So a pump that is going bad can have a low voltage?
It doesn't sound like a bad fuel pump, but if the internals are shorting out or causing a high current draw, voltage will decrease.

But it could simply be a circuit fault in this case causing low voltage. Maybe a bad connection that heats up over time and causing the pump to either barely run or shut down.
 

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Discussion Starter #53
I took some videos Friday, and will post them later today. It seems lkie my return system isn't working right. but after taking it apart 3 times, with different springs every time, It is no different. I didn't get a chance to do the voltage test. Would a bad pump relay cause voltage issues?
 

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I would say that it is probably uncommon, but wouldn't be hard to rule out. Try swapping the relay and see how it goes.
 

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Discussion Starter #55
Still haven't had a chance to check on the voltage, and I'm having eye surgery tomorrow, so I probably wont get to it until Tuesday, but I figured I'd throw these videos up here to see if anyone has any ideas.
Prior to doing this test, I did as RT recommended and filled a 2 gal gas can with fuel and ran a line directly from this can to the intake side of the factory fuel pump. I placed this can on the floor in the cab so I could monitor it. I did not make it 2 miles before running out of fuel. THE CAN WAS EMPTY!!
Fuel pressure during the "jerry can ride" was terrible.

I then re-filled the can, went back to the truck, and drove it back to the house.

I disconnected the return line at the quick connect located near the firewall. I ran a clear line from here to a 5 gal bucket. I also ran my intake line from a 5 gal bucket. The videos show the results. It doesn't make much sense to me.


https://www.youtube.com/watch?v=K8HjOG8xzoQ
https://www.youtube.com/watch?v=V_yJj3-dIhE
https://www.youtube.com/watch?v=NbOffkSaNX4
 

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That's GOTTA be a fuel return regulator issue. The regulator just isn't holding enough back pressure on the system before it lets the fuel out the return line. The FRX kit has a very small bleed hole that lets fuel out of the rails just to keep them from being dead-headed, so the bulk of that fuel coming out your return line on that bucket test has to be coming thru the regulator. Did you check the seat on the regulator plunger?
 

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OK - that tells me everything I need to know.

The way the system works - as I'm sure you know, but I want to put it into words so that we can rule in / rule out stuff:

Fuel pump delivers fuel to the bowl. Everything in excess of the pressure of the FPR spring in the FPR goes back to the tank. That means - if you are at or below the set fuel pressure of the FPR - ZERO/NOTHING/NADA should be coming out of the return line. If you are above the level set at the FPR - whatever is required to maintain the pressure at the set point is shunted through the return line.

You should have NOTHING coming through your return line if the FPR is working correctly and the pressure is below your setpoint. On my truck, that is 62 psi. I have 62 psi cold, 62 psi hot, 62 psi at idle, 62 psi running down the street - the only time it drops below 62 is WOT with a loaded trailer - at which time my pump can't keep up with the demand - even then, it only dips down to about 58 psi...

Your FPR is not working. It isn't seating - at all. Something is keeping it from returning to the seated position with 62 (or whatever spring you are using) psi worth of resistance.
 

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Discussion Starter #58
I've taken the FPR apart 4 times now. I've tried different springs, and different valve bodies (not sure if thats the right term see pics)






I have checked o-rings and seals. I cant figure out what could possibly be wrong. I fully agree with you RT, but I dont really know where to go from here.
 

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OK - I watched the 2nd video again - paused it on the frame where you show your FRx kit - I want to verify something.

It appears you have your "return line" to the bucket plumbed into one of the input lines on top of the regulator. That won't work. Thats "pre plunger" pressure. Your return line should be on the fitting that goes back to the tank. Also, if you have that fitting open, where are the lines that go to the heads? Why aren't they spewing fuel? Can you confirm you installed the kit correctly? Two stainless steel braided lines from each of those two ports on top going to each head (opposite of where the stock fuel line goes in)?

http://www.riffraffdiesel.com/mm5/RESOURCES/Riffraff_Diesel_FRx_Instructions.pdf
 

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Discussion Starter #60
The new FRX kit still uses stainless braided lines, but they are covered in a black sleeve to look more factory. I did not tamper with these lines at all. They are still connected to my cylinder heads per the installation instructions. I tied into the return system at the quick disconnect located near the firewall on the drivers side.
I used a male quick connect I removed from one of my replacement pumps to adapt to the 3/8 ID PVC hose.
 
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